Wireless-telephone receiving system



I'NVENTOR A RNEY PETER wuum WILLANS BY j P. w. WILLANS Filed Oct. 14, 1925 Nov. 12, 1929.

WIRELESS TELEPHONE RECEIVING SYSTEM Patented Nov. 12, 1929 UNITED STATES PATENT orrica PETER WILLIAM WILLANB, OF TOWCES'I'EB, ENGLAND, ASSIGNOB, BY HES ASSIGN- MENTS, TO RADIO CORPORATION OF AMERICA, 01' NEW YORK, N. Y., A CORPORA- rron or nmwaaa WIBELESS-TMPHOI IE RECEIVING SYSTEM 7 Application filed October 14, 1885, Serial Io. 68,471, and in Great Britain October 14,1924

This invention relates toreceiving systems suitablefor use in wireless telephony.

Morei'particularly the invention relates to audio frequency theremionic valve amplifiers for use "in such receivin systems. I have found that the distortion which usually occurs in valve am lifiers is due to three main causes :--(1) he drop in impedance of the intervalve transformer at 10 low frequencies, due to thefact that its inprimary is connected in the anode circuit of, the valve, has its wmdm'gs in opposite sense,

i. e. at the same instant the polarities of the high potential ends of the windings are in ap roximate opposition of phase, and an impe ance is included in the grid circuit in series with a source of electromotive force. The high potential of this impedance is connected through a second impedance to the high po tential of the transformer secondary.

The nature of the impedances depends upon the effect it is desired to produce; but

in general the first impedance is preferably a resistance. In this case, if the second impedance be a condenser, the effective self ca- 7 effects simultaneous y.

pacity' of the transformer will be reduced over a -range of'frequencies and may even attain a zero .or negative value. If an m-,

ductance is used, theeifective inductance of the transformer willbe increased. A combination of the two in arallel produces both The impedance shouldibe large in comparison with the re.-

sistancelat all frequencies concerned.

If the second impedance be itself a resistance, an increase in the iii-phase compo-- nent'of amplification is produced.

If a resistance be combined in parallelwit-h I an inductance and a capacity, the several eifltlacts will be obtained independently of each ot er.

If an inductance is connected in series with a resistance, the effect of magnetic leakage is counteracted.

The effect of magnetic leakage may also be counteracted by means of a reaction transformer, so arranged as to introduce into the rid circuit a voltage sufficient to compensate or that dropped in the anode circuit, owing to the leakage inductance of the intervalve transformer.

The invention is illustrated in the accom-. panying drawin In these drawings 1 is the primary and 2 the secondary ofan intervalve transformer. 3 is the plate, 4 the rid and 5 the filament of an amplifying va ve 6. For the sake of clearness, anode, grid and filament batteries have been omitted from most of the drawings,

as the application of these batteries is well' known.

Referring first to Figure 1, this shows an arran ement in which an impedance 7 is connected in thegrid circuit of the valve 6. The primary and secondary of the intervalve transformer are wound in opposite sense, and the high potential of the secondary is connected through an impedance 8'to the grid 4'. The impulses to be amplified are re resented by an alternating current sign, an the load on the transformer by a capacity 9.

Various results can be obtained according to the nature of this impedance 8. Hit be a capacity, the result will be to reduce the eifective self capacity of the transformer over a range of frequencies; if it be an inductance,

the result will be to increase the effective in ductance of the transformer; an impedance comprising an inductance and capacity in parallel gives both results simultaneously; if it be a resistance, the eifect is to increase the sistance in parallel with an inductance and capacity gives all these results independently of one another; while, aresistance in series with an inductance, compensates for the effect of-magneticleakage. Obviously the exact nature offthe impedance will depend upon thenature of the intervalve transformer, whose distortion is to be compensated for.

Figure 2 shows an arrangement in which the effect of magnetic leakage is compensated for by means of a reaction transformer. The effect of magnetic leakage may be regarded as though it were caused by a separate inductance, shown in the figure as an imaginary inductance 10, in series with the primary of the intervalve transformer, the Wind-- ings thereof being regarded as close-coupled. The eifect of the leakage inductance is compensated for by a reaction transformer whose primary 11 is connected in series with the primary of the intervalve transformer, and whose secondary 12 is connected in the grid circuit.

r If m is the voltage factor of the valve, then the reaction transformer should be such as to introduce into the grid circuit a voltage equal to itimes-that dropped in the leakage inducting should be made equal to the leakage in- Y ductance divided by m--1.

- This arrangement has the disadvantage that the reaction transformer which is normally small tends to oscillate at its own frequenc and for this reason it is preferable to provi e a damping resistance connected across the windings of the said transformer. I have found such a damping resistance to result in practice in a very considerable improvement. Figure 3 shows an arrangement in which means are provided for compensating for all the forms of distortion likely to be occasioned by an intervalve transformer. The grid 4 is connected through the secondary 12 of a reaction transformer, the secondary 2 of the intervalve input transformer, a variable high resistance 13 and a battery it to the filament 5; the anode circuit contains, in addition to the primary 1 of the output intervalve transformer, the primary 11 of the P input to said valve, a second circuit for the 'output from said transformer,

reaction transformer. The high potential of the secondary 2 of the output intervalve transto former, which secondary is wound in the opposite sense to the primary, is connected to the grid circuit between the input intervalve transformer and the resistance 13 through an impedance 8 comprising a capacity an inductance and a resistance, all in parallel with one another. I

It will be apparent that the electrical constants and characteristics of the in at intervalve transformer will have 2. mar ed influence upon the necessary values of the various impedances. For'this reason, and owingto the complexity of the net-work of .which'the impedances form part, it is referable to make the said impedances varia le.

It will be apparent to those skilled in the h vments herein described are possible. For example, in a modification of the arrangement shown in Figure 3, the impedance 8 is a substantially pure resistance, and the resistance 13 is replaced by a small inductance and a large capacity in series.

The invention may also be applied to impedance or choke coupled valves, for the purpose of compensating for distortion, due to the impedance or choke.

The arrangements as hereinbefore described may also be employed for line telephone systerms. for example, in repeater and the like amplifying stations, and for both line and radio telegraph systems.

Having, described my invention what- E claim is 1. In combination a thermionic amplifying valve, an input circuit for said valve, an output from said valve, said output including a transformer, and means comprising a resistance, an inductance and a capacity arranged in parallel connecting said output with said input circuit for compensating for distortion in said transformer.

2. In a valve amplifier, in combination a thermionic valve adapted to operate at audio frequencies, an audio' frequency transformer connected with its primary in the plate cir 'cuit of said valve, an audio frequency input to said valve, an output from said transformer, and means comprising an inductance and a capacity arranged 'inparallel connected between said output and said audio frequency input'for compensating for distortion in said valve amplifier.

3. An amplifying unit comprising a thermionic valve, a transformer connected in the plate circuit of said valve, a circuit for the input to said valve, asecond circuit for the output from said transformer, and an impedance including an inductance connected be tween said input and output circuits.

4. An amplifying-unit comprising a thermionic valve, a transformer connected n the late'circuit'of said valve, a circuit for the and an impedance comprising a capacity, a resistance and an inductance arranged in parallel connected between said input and output circuit.

5. In a valve amplifier, in combination a thermionic valve, 2. grid circuit for said valve, 9. plate circuit for saidvalve, an output cucult, an intervalve transformer coupling said plate circuit to said output circuit, an impedance connecting said output circuit with said rid circuit and a second transformer couphng said plate circuit with said grid circuit. said impedance connection and said second transformer coupling acting to compensate for distortion in said valve amplifier.

PETER WILLIAM -WILLANS. 

